🍒 [6.2] [cxx-interop] Avoid unchecked recursion when importing C++ classes with circular inheritance #81212
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…th circular inheritance It is possible for a C++ class template to inherit from a specialization of itself. Normally, these are imported to Swift as separate (unrelated) types, but when symbolic import is enabled, unspecialized templates are imported in place of their specializations, leading to circularly inheriting classes to seemingly inherit from themselves. This patch adds a check to guard against the most common case of circular inheritance, when a class template directly inherits from itself. This pattern appears in a recent version of libc++, necessitating this patch. However, the solution here is imperfect as it does not handle more complex/contrived circular inheritance patterns. This patch also adds a test case exercising this pattern. The -index-store-path flag causes swift-frontend to index the C++ module with symbolic import enabled, without the fix in this patch, that test triggers an assertion failure due to the circular reference (and can infinitely recurse in the StorageVisitor when assertions are disabled). rdar://148026461 (cherry picked from commit 1f2107f)
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@swift-ci please test |
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@swift-ci please test macos |
egorzhdan
approved these changes
May 1, 2025
DougGregor
approved these changes
May 2, 2025
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Explanation: This patch adds a check to guard against unbounded recursion when importing class templates that inherit from a specialization of themselves, a pattern appears in libc++. The unbounded recursion only happens with symbolic imports enabled, which is why this was not caught before.
Issue: rdar://148026461
Risk: low
Testing: added a new test case
Original PRs: #81188
Reviewer: @egorzhdan